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What Are Lice, and Where Do They Come From?

What Is Lice?

The head louse (plural, lice) is
scientifically known as Pediculus humanus capitis, and an infestation with head lice is medically
known as Pediculosis capitis.

Head lice are obligate parasites. This means that they cannot survive
without a human host—this species can live only on human hosts, so you cannot
get them from your dog, cat, guinea pig, or any other kind of furry pet you may
have.

Head lice have no wings, so they cannot fly. They have six legs with
claws at the ends—that is how they attach themselves to hair.

Head lice infestations can happen
to anyone, but they are a particular concern for school-age children. It is
important to emphasize that poor hygiene, skipped baths or showers, or any
other hygiene issue is not the cause of head lice. Children who live in crowded
conditions may have more of a problem with head lice, but that is only because
they are living close to one another and may sleep in the same bed. The only
way head lice spread from one person to another is by direct head-to-head
contact (as when kids hug or put their heads together to look at the same book)
or by the sharing of hats, caps, hair ties, scarves, or any personal item such as
combs or brushes.

Female adult lice can lay three to
four eggs every day. The eggs are laid about 3 to 4 millimeters from the scalp,
right onto the shaft of hair. The eggs are essentially glued on by secretions
from the female louse. The eggs take about a week to hatch—producing a nymph. The
nymphs then go through three successive growth spurts, during which they molt—the
most obvious effect is an increase in size until they reach adult size. Adults
are about the size of a sesame seed—and can be very hard to see because they
can be any color from white to tan to brown.

Lice feed on blood—they use their
mouth parts to bite into the skin and secrete a substance that acts to block
clotting. They feed about four to five times every day.

Head lice can be found anywhere on
the scalp, but are commonly found on hairs at the back of the neck and around
the ears.

There are a number of treatments
that can effectively get rid of head lice—these include over-the-counter (OTC)
products, natural products, and prescription medications.

The advantage to some of the
natural products is to avoid the potential safety issues of using insecticides
on small children. A number of studies have shown that some natural products,
including those using tea tree oil, eucalyptus oil, neem oil, and lavender oil,
can be just as effective as OTC products.1-4
In addition, lice seem to be getting resistant to some commonly used products.5,6

Body lice are a bit different from head
lice. They lay their eggs on clothing instead of on the body. Body lice can
carry a number of diseases, including louse-borne typhus, relapsing fever,
trench fever, and bubonic plague.7

3. Barker SC,
Altman PM. A randomised, assessor blind, parallel group comparative efficacy
trial of three products for the treatment of head lice in children—melaleuca
oil and lavender oil, pyrethrins and piperonyl butoxide, and a
"suffocation" product. BMC Dermatology
2010;10:6-.

4. Treatment of
head lice. The Medical Letter on Drugs and
Therapeutics 1980;22:66-8.

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